Internet services are often deployed in multiple geographically distributed locations, so that they can be close and deliver fast and responsive services to clients. To improve client performance, a particular data center may be dynamically determined for each individual user. By serving users from the particular data center (e.g. a data center close to a location of the client or a data center with low latency with respect to the client or an ISP of the client), content such as web search results, Internet videos, online gaming messages, and software updates may be delivered with low latency and high throughout while reducing network congestion. However, the “best” data center for a client may correlate poorly with geographic distance from the client. Instead, the “best” data center may be determined by a combination of network latency, packet loss, and available bandwidth. In addition, the identity of the “best” data center for a client may be dynamic and may change with Internet routes, service providers, and physical network connectivity.